Thermal characterization of wood of nine European tree species: thermogravimetry and differential scanning calorimetry in an air atmosphere

This paper presents a thermal characterization of hardwoods of Hungarian origin. The study covers the wood of the following tree species: sessile oak (Quercus petraea), beech (Fagus sylvatica), hornbeam (Carpinus betulus), black locust (Robinia pseudoacacia), lime (Tilia platyphyllos), ash (Fraxinus ornus), maple (Acer campestre), alder (Alnus glutinosa), and aspen (Populus tremula). Wood samples were subjected to differential scanning calorimetry and thermogravimetry in an air atmosphere at different heating rates of 10, 20, and 40 °C·min−1. The activation energy was calculated using the Flynn–Wall–Ozawa method. Thermogravimetric analysis revealed that tree species differed considerably in the mass loss and the temperature of the maximum mass loss rate related to the thermal degradation of the main wood components and the oxidation of char mainly derived from lignin. Beech, hornbeam and ash were characterized by a high mass loss attributed to decomposition of hemicelluloses. The mass loss assigned to the thermal degradation of cellulose varied from 35.41% (ash wood) to 53.65% (alder wood). Sessile oak wood showed the greatest mass loss and the highest temperature of thermoxidation of residual lignin and char. Calorimetrically measured values of the exothermic effect of the wood thermal degradation were in the range 7.93–9.65 kJ g−1. The average values of activation energy for the thermal degradation of carbohydrates and the thermoxidation of residual lignin and char were found to be 176.0 ÷ 197.3 kJ mol−1and 196.4 ÷ 319.5 kJ mol−1, respectively.